摘要:

SummaryThe LT50(lethal temperature) of first instar and adult stages of the peach‐potato aphid Myzus persicae was lowered following long term acclimation at low temperatures.First instars consistently showed greater cold hardiness than adult stages at each acclimation temperature, with the differential increasing as the temperature was lowered. When maintained at 5°C (the lowest acclimation regime) nymphs and adults had dLT508.3°C and 4.7°C respectively lower than those for non‐acclimated individuals.When 10°C acclimated adults were returned to 20°C, the acclimation effect was retained in full for 6 days but complete deacclimation occurred by day 10. In contrast the LT50of their progeny increased gradually from the first day of adult deacclimation towards the level of the unacclimated control over a period of 10 days.A change in cold hardiness was observed in first instars according to their position in the birth sequence. The LT50of first‐born nymphs (day 1 of reproduction) from 20°C parents was ‐ 15.9°C rising to ‐ 8.3°C by day 4 and remaining at this level until the end of the reproductive period.The differential mortality between nymphs and adults observed in the laboratory was supported by the results of a field experiment. Adult aphids kept in clip‐cages on a crop of oilseed rape showed greater mortality compared with those introduced as nymphs when the minimum temperature fell below ‐4°C for the first time in winter. At ‐ 10°C mortality of aphids introduced as adults approached 100% whereas more than 50% of those introduced as nymphs were still

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06581.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryA braconid parasitoid Heterospilus prosopidis was contaminated with either Colletotrichum coffeanum or C. gloeosporioides, causal agents of coffee berry disease and mango anthracnose respectively. Adult parasitoids could collect wetted and unwetted spores of both pathogens on their bodies. Viable spores were recovered in washings from these insects 10 days after infestation. Wetted spores of both species of pathogen had lower viability on the parasitoid's body than unwetted spores, probably because of the loss of the mucilage coating which protects against desiccation. The results suggest that the use of a related parasitoid, H. coffeicola, in biological control against the coffee berry borer, Hypothenemus hampei could pose a phytosanitary risk.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06582.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryA map of the geographic distribution of leather jackets across five counties of Northern Ireland was produced from annual survey data. Climatic data were used to develop a multiple regression model explaining variation in the mean annual survey population for the years 1970–1984. Predicted populations for 1985–1988 compared favourably with observed counts. Both negative binomial and Adès distributions were successfully fitted to the frequency distribution of leatherjacket field populations from 1969–1986. It is concluded that the distribution of populations in the Province is not random and factors influencing mean leatherjacket numbers differ from those reported for other regions. The multiple regression model is proposed as a substitute for an annual survey of leatherjacket populations in Northern Ireland and it is suggested that the Adès family of distributions may enable it to be extended to predict leatherjacket frequency distributions ea

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06583.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe toxicity (LD,) of eight insecticides to 2–day‐old first instar larvae of Pieris brassicue was determined by topical application. On this basis, the insecticides could be ranked in ascending order viz. dimethoate>pirimicarb>phosalone>endosulfan>fenitrothion>pirimiphos‐methyl>fenvalerate>diflubenzuron. Relative to endosulfan, dimethoate and pirimicarb were 30–25 times less toxic while at the other extreme, fenvalerate (x 12) and diflubenzuron (x 26) were much more toxic to the larvae of P. brassicae.A methodology was developed for examining the effects of spray drift through bioassay using these 2–day‐old larvae. Six field trials with commercial formulations were carried out in which variables other than the insecticide and wind speed were held constant as far as possible. Phosalone (700 g active ingredient ha) produced no effect beyond 1 m downwind at low wind speed (2 m s); at high wind speed (4 m s‐1). larval mortality (5.3%) was recorded up to 2m. Fenitrothion (1050 g a.i. ha‐1) at moderate wind speed (3 m s‐l) caused mortality up to 4 m while fenvalerate (30 g a.i. ha‐l) at the same wind speed affected larvae up to a distance of 8 m. Diflubenzuron at a very low dosage (6.5 g a.i. ha‐1) also produced effects up to 8 m. At the maximum approved dosage (100 g a.i. ha‐1), and at high wind speed (4.25 m s‐l), diflubenzuron killed 8.4% of the larvae at 16 m distance.At wind speeds of 2 ‐ 3.5 m s‐1, spray deposits on the upper surfaces of water sensitive papers were high at 0 m and declined exponentially with distance. At higher wind speeds (4 ‐ 4.25 m s‐I) turbulence produced irregular deposits. Deposition on lower surfaces was much lower than on upper surfaces but the trends with distance and wind speed were the same.The exponential relationships between mortality and distance, and drift deposition and distance, were examined. The results are discussed with respect to laboratory toxicities, application rates, w

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06584.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThree inoculation techniques for Karnal bunt (Tilletia indica) disease of wheat were compared: 1) boot inoculation ‐ injection of inoculum with a hypodermic syringe into the boot; 2) spray inoculation ‐ inoculum sprayed at growth stages between heading and anthesis, and 3) cotton wool inoculation ‐ small pieces of cotton wool saturated in inoculum placed either inside the floret or between the spikelet and rachis. Each inoculation technique was assessed using susceptible cultivars to determine the optimum inoculum concentration, the ideal plant growth stage and the humidity requirements for successful infection.Boot inoculation did not require high humidity and gave reliable infection with low secondary sporidia concentrations (1000–10 000/ml). The ideal plant growth stages for inoculation were early‐boot and mid‐boot. Spray inoculation required high secondary sporidia concentrations (50 000/ml) and 48 h of high humidity, but infection was initiated over a range of growth stages throughout heading and anthesis. Cotton wool inoculation gave low levels of infection at growth stages throughout heading and anthesis, even with high secondary sporidia concentrations (

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06585.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryAn assessment was made over 3 years of the efficacy of thiabendazole, 2–aminobutane and a formulation of a mixture of thiabendazole and 2–aminobutane in controlling gangrene, skin spot and dry rot when applied either at harvest or after grading at different dates during the storage season.After harvest applications, the incidence of gangrene was least on tubers treated with the mixture and generally greatest with thiabendazole. When applied after grading the efficacy of the fungicides was not affected by date of grading. Although 2–aminobutane applications at harvest or after grading were equally effective in controlling gangrene, thiabendazole and the mixture were less effective after grading where gangrene was prevalent in a stock. Thiabendazole and the mixture gave good control of dry rot when applied at harvest but were less effective when applied after grading, particularly late in the storage season. Dry rot was sometimes more prevalent on tubers fumigated with 2–aminobutane, especially those treated after grading. Skin spot was more effectively controlled by the mixture and 2–aminobutane than by thiabendazole but, with applications after grading, the efficacy of all fungicides declined the later the date of grading.Plants grown from tubers treated with the mixture or its 2–aminobutane glycollate constituent exhibited characteristics associated with geneti

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06586.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryIn Western Australia, infection with cucumber mosaic virus (CMV) was widespread in all three subspecies of subterranean clover (Trifolium subterraneum) growing in plots belonging to the Australian National Subterranean Clover Improvement Programme. Seed‐borne CMV was detected in seed harvested in 1984–1986 of 18/25 cultivars from two collections of registered cultivars; seed transmission rates ranged up to 8.8%. Seed samples from CMV‐inoculated plants of 11 cultivars transmitted the virus to 0.5–8.7% of seedlings. Seed transmission rates greater than 5% were obtained only with cvs Enfield, Green Range and Nangeela. CMV was not detected in seed harvested in 1975–1981 from one of the registered cultivar collections, in 17 commercial seed stocks from 1986 or in a survey of subterranean clover pastures.Symptoms in subterranean clover naturally infected with CMV included mottle, leaflet downcurling and dwarfing but severity varied with cultivar and selection. CMV isolates from different sources varied in virulence when inoculated to subterranean clover; two (both from subterranean clover) were severe, two moderate and three (including one from subterranean clover) mild. In pot tests, CMV decreased herbage production and root growth (dry wts) of cv. Green Range by 49% and 59% respectively. In spaced‐plants growing in plots, CMV decreased herbage production and root growth of cvs Green Range and Northam by 59–630 and seed production of cv. Green Range by 45%. In rows sown with infected seed, aphid spread increased infection levels to 75% in cv. Green Range and 44% in cv. Esperance and losses in herbage production of 42% and 29% respectively were recorded.CMV isolated from subterranean clover included isolates from bo

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06587.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryTwo approaches based on the concept of a vector population index are considered as possible deterministic elements for an empirical forecast of barley yellow dwarf virus (BYDV) in autumn sown cereals. The first, an aerial vector index, is a further elaboration of the infectivity index proposed by Plumb, Lennon&Gutteridge (1981), which assumes that virus damage is a function of the number of infective migrant alatae of the two main aphid vectors, Rhopalosiphum padi L. and Sitobion avenae F., integrated over time from crop planting or emergence. The new formulation, however, excludes holocyclic alate morphs (i.e. males and gynoparae) of the former species, which, although generally abundant in autumn, are nevertheless perceived as relatively unimportant virus vectors since they colonise only the alternative woody host, Prunus padus (the bird‐cherry tree). The second approach, a crop vector index, is a more fundamental departure which argues that field populations of viruliferous aphids, both alatae and apterae, which have already colonised cereals, may be a better criterion of potential virus spread than the density of aerial migrant vectors. This index retains a similar integral form, but evaluates crop exposure to BYDV as accumulated infectious aphid‐days. A method is described whereby this function can be derived from irregular or infrequent aphid samples in the crop. Both methods, unlike Plumb's (1976) original concept, produced indices which were significantly related to subsequent virus infection and yield loss in winter barley at Long Ashton (S.W. England, UK), 1978–1986. The best models were obtained with the crop vector index, fitted to observed virus infection by generalised linear regression using a complementary log‐log link function, or to observed yield loss by simple linear regression using a log transformation of yield (r = 0.84 in each case; compared with r‐values>0.65 for the aerial vector index, and>0.35 for Plumb's (1976) index). However, the residual errors and hence confidence limits of these fitted regressions were too large for predicting damage that was significantly less than a reasonable economic damage threshold for BYDV control.Analyses of the separate components of each index showed a good general relationship between aphid infectivity and the severity of crop infection, confirming the epidemiological importance of this factor. The functional expressions of aphid density, however, were not significant. This evident weakness in the models, and alternative approaches to BYDV forecasting are

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06588.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryWestern Australia has a unique seed potato production scheme which has remained virtually unchanged for more than 60 years, consisting of summer plantings of predominantly one cultivar in wind‐exposed coastal swamplands. No rotation is used and the scheme relies on natural winter flooding and ‘grazing’ by sheep to eliminate unharvested tubers. Stocks are recycled every year with only limited inputs of pathogen‐tested seed tubers in recent times. Virus spread in the crop is controlled by selecting large tubers for planting, roguing, aphicide application and growing season inspections. Potato viruses X and S were commonly detected in old seed stocks produced by this scheme attaining 100% infection in some. Both viruses were less frequently found in newly introduced seed stocks. By contrast, potato virus Y was never detected and potato leaf roll virus rarel

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06589.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryFour methods of spray application were compared in 1986 with the recommended method of glyphosate application for pre‐harvest retting of flax (Linum usitatissimum). Sampling individual plants immediately after application of glyphosate and dye demonstrated that spray penetration through the crop canopy, measured as dye deposition on the lower stem as a percentage of total deposition per plant, was the same for all methods of application. None of the methods of application improved the uniformity of dye deposition.The following year, effects of deseeding prior to spraying and of using an air‐assisted sprayer were investigated. Deseeding increased dye deposition on the lower stem but did not improve the efficacy of glyphosate. Application with an air‐assisted sprayer increased the proportion of spray deposited on the lower stem but not the absolute amount deposited or the efficacy of glyphosate. Dye deposition on individual plants varied greatly for all methods of application and, when glyphosate was applied using the same methods, undesiccated plants occurred in all plots.Considerable improvements in spray penetration and uniformity of spray deposition appear necessary for successful pre‐harvest retting of flax with gly

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb06590.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY